Power array for high power pulse load

ABSTRACT

A controlled power supply comprising: a) an array of low voltage current sources; b) a plurality of switch power supplies coupled to each of the storage capacitors and respective ones of the pulse loads being coupled to each of the switch power supplies; c) each of the storage capacitors being configured for storing energy during an inactive portion of a load switching cycle of the respective switch power supply to which the corresponding storage capacitor is coupled when the pulse loads are inactive; d) a respective output capacitor in association with each of the switch power supplies for feeding voltage to the respective pulse loads during an active portion of the load switching cycle; and e) the respective storage capacitor being configured for supplying the stored energy via the respective to the respective switch power supply to which the storage capacitor is coupled to each of the pulse loads coupled to switch power supply during an active portion of the load switching cycle.

RELATED APPLICATIONS

This application is a 371 of PCT/IL08/01662 filed Dec. 24, 2008, whichclaims priority under 35 U.S.C. 119 from ISRAEL Application No. 188477filed on Dec. 27, 2007, the contents of which are incorporated herein byreferences.

FIELD OF THE INVENTION

This invention relates to pulse load switching power supplies that isparticularly suitable for use in phased array radar antennas.

BACKGROUND OF THE INVENTION

Some types of phased array antennas require that a large numbers ofantenna elements be activated simultaneously. This, of course, demandssignificant power, which is provided by the main system power supplies.The incremental contribution that each antenna element makes to thecomposite beam is, of course, a feature of the antenna design and so itis possible to determine in advance which antenna elements to energizeand at what voltage magnitude in order to achieve a desired beamsteering and tracking. Each antenna element is energized according tothe pulse width to be transmitted so that there is an instantaneousdemand for the time period when the antenna element is active followedby an inactive period when the antenna elements are waiting for the nexttransmitting pulse. However, the sudden current surges thus consumedwhen the antenna element becomes active place a severe demand on thesystem power supplies. It is therefore clearly desirable to energize theantenna elements in such a manner that the current surges are reduced.

It will be apparent from the foregoing discussion that each antennaelement operates as a pulsed or switched load which requires a largesupply of power intermittently. Conventional solutions using switchingmode power supplies for such a load struggle to avoid the output voltagedropping during the transmission pulse and reflecting the load powerrequirements to the main system power supplies. The ripple current inthe current supplied by the main power supply can cause high radiofrequency interference RFI which is reflected on to the main supplysource if it is not suppressed.

The circuit that converts source input voltage DC to pulsed AC is knownas a switching converter or simply ‘converter’ of which there are twoprincipal types, ‘Buck’ and ‘Boost’ although there are several hybridsand variations. The Buck converter normally converts the voltage down sothat the output voltage of the converter is lower than the input voltageto the converter by a factor δ that is equal to the duty cycle of theswitch. Duty cycle is the ratio between the duration during each cyclethat the switch is ON to the total time between successive pulses, i.e.the period, i.e.

V_(OUT) = δ ⋅ V_(IN)$\delta = {\frac{T_{ON}}{T} = \frac{T_{ON}}{\left( {T_{ON} + T_{OFF}} \right)}}$where:

V_(IN)=input voltage;

V_(OUT)=input voltage;

δ=Duty cycle

T_(ON)=Time when switch is ON

T_(OFF)=Time when switch is OFF

T=Pulse period=(T_(ON)+T_(OFF))

The Boost converter converts the voltage up so that the output voltageof the converter is higher than the input voltage by a factor

$\frac{1}{1 - \delta},$where δ is equal to the duty cycle of the switch. Since δ is less than1, this factor is greater than 1.

It thus emerges from the foregoing discussion that regardless of thetype of converter that is employed, the output voltage of the converteris a function of the duty cycle of the switch. This allows accurateregulation of the voltage simply by controlling the duty cycle of theswitch voltage, and this is easily achieved using pulse widthmodulation, PWM to control the pulse width during which the switchingvoltage pulse is ON. Since the period of the switching voltage pulseremains constant, adjusting the pulse width of the ON time varies theduty cycle of the switching voltage.

US 2004/178950 discloses a method of controlling a switching element ina switching regulator power supply of a radar. The method of controllingthe switching element comprises only switching the switching elementduring predetermined time intervals, the predetermined time intervalsadvantageously being sample intervals of a pulse repetition interval ofthe radar. Thereby by having knowledge of the time intervals theswitching element is switching, being able to remove or diminish anyinfluence the switching can have on the quality of received signals andsubsequent processing of these signals.

US 2004/062058 discloses a power conversion unit and method forefficient conversion of power for one or more variable loads such as aradar system. Power having a first form is supplied to one or more powerconversion units (PCUs) connected to the one or more variable loads. ThePCUs are adapted to convert the power from the first form to other twinssuitable for use by the components of the destination system. Based atleast in part on a predicted load requirement of the variable load, theoperation of the PCUs can be controlled to provide sufficient power tothe one or more loads at the appropriate time while minimizing wastedpower generation by deactivating any unnecessary PCUs during a decreasein power consumption or by activating PCUs during an increase in powerconsumption. Additionally, based at least in part on a predictedtemporary change in the load requirements, the PCU can change its outputvoltage in anticipation of the temporary change in the load requirement,such as by increasing the output voltage to provide additional energy tothe one or more variable loads during a temporary increase in powerconsumption or by decreasing the output voltage during a temporarydecrease in power consumption.

U.S. Pat. No. 5,418,708 discloses a constant power load bank forsimulating avionics loads such as pulsing radars on a 270 VDC powersystem. The load bank is designed to realistically simulate an activeaperture radar with 0-100% of the load pulsing while the remainder ofthe load is either on or off. The pulse controls are designed tosimulate any type of pulsing scenario from simple (one control signal)to complex (multiple control signals simulating incremental loadapplication and removal such as an active aperture radar load).

IL 181843 entitled “Controlled power supply and method for pulse load”by the same inventors of the present application and filed Mar. 11, 2007in the name of the present applicant discloses a method and a controlledpower supply for supplying bursts of substantially constant voltage to aswitched load via a voltage reservoir, typically constituted by astorage capacitor. Based on a predetermined current that is to besourced by the load during an active portion of a switching cycle, anaverage current is computed that should be fed to the voltage reservoirduring an inactive portion of the switching cycle to ensure thatsufficient energy will stored in the storage capacitor to supply theload without completely draining the storage capacitor. Continuousenergy is fed to the storage capacitor at a substantially constantcurrent equal in magnitude to the computed average current.

The complete contents of all the above references are herebyincorporated herein by reference to the extent that they provide usefulbackground. However, since the present invention is a specificapplication of the power supply described in IL 181843, which has notyet been published, the relevant details of IL 181843 will be describedsubstantially verbatim so as to provide a completely enablingdescription.

In the related art, an RFI filter at the input of the power supply isused to filter the radio frequency interference so that RFI is notreflected on to the main supply source. Maintaining the ripple currentas low as possible also diminishes the conduction losses related to highroot mean square (RMS) current values, which reduce the current deliverycapability of the supply source. However, when a switch power supply isused in conventional circuits for supplying power as intermittentcurrent bursts, the sudden current burst reflects on the line causingsudden and intermittent voltage reductions on the line. When very highpower bursts are being supplied, the RFI filter becomes bulky andexpensive.

FIG. 1 shows the topology of a conventional prior art power supply array10 for feeding DC power to antenna elements 11 of a phased array antennaand FIG. 2 is a table showing typical parameters associated with thepower supply array 10. In order to provide a radar system that can trackin four directions, four antenna arrays are provided each on arespective “wall” 12, there being one wall 12 for each surface of thesystem as explained above. Each wall 12 comprises an array of highvoltage power supplies 13 that are energized by the system powersupplies and each of which feeds high voltage rectified DC voltage to aplurality of switch power supplies 14 via smoothing capacitors 15coupled at the output of the high voltage power supplies 13 and whichserve to reduce voltage ripple of the high voltage power supplies 13.Capacitors 16 at the input to each of the switch power supplies 14,which may be located remote from the high voltage power supplies 13,serve to decouple the switch power supplies 14 from the high voltagepower supplies 13. Each of the switch power supplies 14 has a respectiveoutput capacitor 17 that feeds voltage to the respective antenna element11 that serves as a pulse load.

FIG. 2 is a table showing a breakdown of the operating parameters of thepower supply array 10 shown in FIG. 1. Thus, starting from the bottom ofthe table each wall 12 accommodates a single phase array antenna, thusresulting in a total of four phase array antennas. Each of the fourwalls 12 houses six high voltage power supplies 13, thus resulting in atotal of 24 high voltage power supplies 13. Each of the 24 high voltagepower supplies 13 is coupled to 27 switch power supplies 14, thusresulting in a total of 648 switch power supplies 14. Each of the switchpower supplies 14 supplies 16 antenna elements 11, thus resulting in atotal of 10368 antenna elements 11. Now working down from the top of thetable, it is assumed that each of the 10368 antenna elements 11 requiresthat the input voltage across the output capacitor 17 of thecorresponding switch power supply 14 is 8.7 volts and it is also assumedthat input current (Iinp) to each antenna element 11 is 9 ampère, thusrequiring an input power (Pin_p) of 78.3 watts to each antenna element11, when active. Assuming a 10% duty cycle, this means that when theantenna element 11 is active i.e. draws power from the switch powersupply 14, the average power (Pin_avg) drawn by each antenna element 11is 7.8 watts. The output power (Pout_p) of each antenna element 11 isassumed to be 20 watts based on the efficiency typically achieved by theantenna elements making an efficiency of 26% since the input power(Pin_p) is 78.3 watts.

Having thus determined the operating parameters of each antenna element11 within each switch power supply 14, we can now work our way down thetable and compute the operating parameters of the switch power supplies14. In like manner, we can then determine the operating parameters ofeach high voltage power supply 13, then of each wall 12 and finally ofthe complete power supply array 10. Although the results are tabulatedin FIG. 2, for the sake of completeness we will now show how the salientresults are derived assuming that the input voltage (Vin) to the antennais 270 volts.

The output power (Pout_p) of each switch power supply 14 is equal to thepower (78.3 watts) fed to each antenna element 11 multiplied by thenumber (16) of antenna elements 11 in each switch power supply 14, i.e.1252.8 watts. The input power (Pin_p) to each switch power supply 14 isequal to the output power (Pout_p) divided by the efficiency, estimatedat 85% this being a typical efficiency of a switching mode power supply,i.e. 1,474 watts. The input current (Iinp) to each switch power supply14 is equal to the input power (Pin_p) i.e. 1,474 watts divided by theinput voltage (Vin) assumed to be 70 volts, this value being selected tokeep the capacitor voltage low enough and avoid large currents, thusmaking the input current (Iinp) equal to 21.1 ampère.

Similarly, the output power (Pout_p) of each high voltage power supply13 is equal to the power (1,474 watts) fed to each switch power supply14 multiplied by the number (27) of switch power supplies 14 in eachhigh voltage power supply 13, i.e. 39,795 watts. The input power (Pin_p)to each high voltage power supply 13 is equal to the output power(Pout_p) divided by the efficiency, again estimated at 85%, i.e. 46,817watts. The input current (Iinp) to each high voltage power supply 13 isequal to the input power (Pin_p) i.e. 46,817 watts divided by the inputvoltage (Vin) assumed to be 270 volts this being approximately equal tothe voltage obtained by a 3-phase full wave rectifier of a 115V system(i.e. 115*√{square root over (2)}*√{square root over (3)}), thus makingthe input current (Iinp) equal to 173.4 ampère.

By similar reasoning it can be shown that the output power (Pout_p) ofeach wall 12 is equal to the power (46,817 watts) fed to each highvoltage power supply 13 multiplied by the number (6) of high voltagepower supplies 13 in each wall 12, i.e. 280,905 watts. The input power(Pin_p) to each wall 12 is equal to the output power (Pout_p) divided bythe efficiency, estimated at 99% owing to wires and connector losses,i.e. 283,742 watts. The input current (Iinp) to each wall 12 is equal tothe input power (Pin_p) i.e. 283,742 watts divided by the input voltage(Vin), again assumed to be 270 volts, thus making the input current(Iinp) to each wall 12 equal to 1,051 ampère.

Finally, since the complete phase array antenna comprises four walls, itcan be shown that the output power (Pout_p) of the complete antenna isequal to the power (283,742 watts) fed to each wall 12 multiplied by thenumber (4) of walls 12 in the complete antenna, i.e. 1,134,968 watts.The input power (Pin_p) to the complete antenna is equal to the outputpower (Pout_p) divided by the efficiency, assumed to be 100%, i.e.1,134,968 watts. The input current (Iinp) to the complete antenna isequal to the input power (Pin_p) i.e. 1,134,968 watts divided by theinput voltage (Vin), assumed to be 270 volts, thus making the inputcurrent (Iinp) to the complete antenna equal to 4,204 ampère.

Having established the operating parameters of the power supply array 10and its sub-components, we can now calculate the values of thecapacitors 15, 16 and 17 as follows.

The energy stored in a capacitor C charged to a voltage V is given by:E=0.5*C*V ²  (1)

The energy required by a power pulse of amplitude W and duration (width)t_(w) is given by:E=W*t _(w)  (2)

Given that the energy is delivered to the load by discharging the energystored in a capacitor from an initial voltage V_(i) to final voltageV_(f), the amount of energy thus required is obtained by:E=0.5*C*(V _(i) ² −V _(f) ²)  (3)

Assuming that for a pulse transmitter, the allowable time to restore thedelivered energy to the storage capacitor is a single pulse repetitioninterval (PRI), this can be achieved by feeding current from a currentsource into a storage capacitor, so that the integrated current during asingle PRI fully charges the capacitor. In this case, the value of therequired capacitor is given by:

$\begin{matrix}{C = \frac{E}{0.5*\left( {V_{i}^{2} - V_{f}^{2}} \right)}} & (4)\end{matrix}$

This equation assumes that the efficiency is 100%. But in practice theefficiency is less than 100% and therefore equation (4) must be modifiedas follows:

$\begin{matrix}{C = {\frac{E}{0.5*\left( {V_{i}^{2} - V_{f}^{2}} \right)}*\frac{1}{\eta}}} & (5)\end{matrix}$where η is the efficiency. In saying this, it is to be noted that in thefollowing analysis the efficiency, η, does not refer to the efficiencyof the capacitor, which is assumed to be 100%, but rather to theefficiency of power conversion between the high voltage power supplies13 and the switch power supply 14 to which the output capacitor isconnected. This distinction is important because when the initialvoltage V_(i) used in equation (4) is directly derived from the voltageof the switch power supply 14, the efficiency, η, may be assumed to be100%. On the other hand, when the initial voltage V_(i) used in equation(4) is derived from the voltage of the high voltage power supplies 13,the conversion efficiency, η, which of course is less than 100%, must befactored in.

By substituting for E from equation (2) into equation (4) we obtain:

$\begin{matrix}{C = {\frac{W*t_{w}}{0.5*\left( {V_{i}^{2} - V_{f}^{2}} \right)}*\frac{1}{\eta}}} & (6)\end{matrix}$

For example if the required output pulse power is 5 KW and thetransmitted pulse is 100 μsec width, and the allowed voltage drop acrossan input capacitor charged to an initial voltage of 70V is 50V (i.e.V_(f)=20V), then using equation (6) and assuming an efficiency η of100%, it can be shown that the value of the required storage capacitoris 220 μF.

We have already determined that in the power supply array 10 shown inFIG. 1, the input power (Pin_p) for each high voltage power supply 13 is46,817 watts. So, by same reasoning, if the width of the transmittedpulse is 100 μsec and the permitted voltage drop across the storagecapacitor having an initial voltage of 270V is 2V, then using equation(6) and assuming an efficiency η of 85%, it can be shown that the valueof the required storage capacitor is given by.

$\begin{matrix}{C = {{\frac{39,795*100}{0.5*\left( {270^{2} - 268^{2}} \right)}\mu\; F} = {7,397\mspace{14mu}\mu\; F}}} & (7)\end{matrix}$

It should be understood that while the efficiency, η of 85% does notappear discretely in equation (7), it is taken into account by virtue ofthe fact that the input power (Pin_p) for the high voltage power supply13 is 46,817 watts, while the output power (Pout_p) is 39,795 watts,which is equivalent to an efficiency of 85%.

In other words, each storage capacitor 15 in the power supply array 10must be rated over 7,000 μF at 300V. Each such capacitor is huge andbulky and there are some 24 such capacitors required in total, i.e. onefor each high voltage power supply 13.

Likewise, assuming that the output capacitor 17 for each antenna element11 operating at 8.7V and an RF output peak power of 20 W and assuming anefficiency η of 26%, may be subjected to a voltage drop of 0.5V and a 15μs recovery time the value of the output capacitor 17 is given by:

$\begin{matrix}{C = {{\frac{20*15}{0.5*\left( {8.7^{2} - 8.2^{2}} \right)}*\frac{1}{0.26}\mu\; F} = {277\mspace{14mu}\mu\; F}}} & (8)\end{matrix}$

The efficiency, η of 26% must be taken into account in equation (8)because the power of 20 W is the output power of the capacitor that isfed to the antenna element, while the initial voltage of 8.7V is derivedfrom the switch power supply 14. Therefore, the efficiency in convertingthe input power (Pin_p) of the switch power supply 14 (i.e. 78W) to theoutput power (20W) fed to the antenna element must be factored in.

In the power supply array 10 shown in FIG. 1 where there are 10368antenna elements 11 in total, some 10368 such output capacitors arerequired.

Yet a further drawback with such a circuit topology where 16 antennaelements are powered by each switch power supply 14 is that failure of aswitch power supply 14 results in 16 antenna elements becominginoperative and this, of course, may impact adversely on the magnitudeand shape of the antenna beam. This drawback may to some extent bemitigated by powering antenna elements that can never be energizedsimultaneously owing to their being on mutually opposing walls amongdifferent switch power supplies. However, while this reduces the adverseeffect of such a failure it still results in multiple antenna elementsbecoming inoperative in the event of a failure in a switch power supply14.

It would therefore be desirable to provide a power supply array forenergizing antenna elements of a phase array antenna wherein muchsmaller input and output capacitors may be used and which lends itselfmore efficiently to independent operation of each antenna element so asto reduce the number of inoperative multiple antenna elements in theevent of a faulty switch power supply.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a power supply array forenergizing a plurality of pulse loads such as antenna elements of aphase array antenna wherein much smaller input and output capacitors maybe used.

It is a further object to provide such a power supply array which lendsitself more efficiently to independent operation of each pulse load soas to reduce the number of inoperative pulse loads in the event of afaulty switch power supply.

According to a first aspect of the invention there is provided a methodfor supplying bursts of substantially constant voltage to a plurality ofpulse loads, the method comprising:

providing an array of low voltage current sources each for feedingconstant DC current at a nominal voltage to a respective storagecapacitor each of which is coupled to a plurality of switch powersupplies;

coupling each of the switch power supplies to respective ones of thepulse loads;

storing energy in each of the storage capacitors during both active aninactive portion of a load switching cycle of the respective switchpower supply to which the corresponding storage capacitor in associationwith each of the switch power supplies for feeding voltage to therespective pulse loads during an active portion of the load switchingcycle; and

supplying the stored energy in the respective storage capacitor via therespective to the respective switch power supply to which the storagecapacitor is coupled to each of the pulse loads coupled to switch powersupply during an active portion of the load switching cycle.

According to a second aspect of the invention, there is providedcontrolled power supply for supplying bursts of substantially constantvoltage from a voltage reservoir to a plurality of pulse loads via aload switch, said power supply including:

an array of low voltage current sources each for feeding constant DCcurrent at a nominal voltage to a respective storage capacitor;

a plurality of switch power supplies coupled to each of the storagecapacitors and respective ones of the pulse loads being coupled to eachof the switch power supplies;

each of the storage capacitors being configured for storing energyduring an inactive portion of a load switching cycle of the respectiveswitch power supply to which the corresponding storage capacitor iscoupled when the pulse loads are inactive;

a respective output capacitor in association with each of the switchpower supplies for feeding voltage to the respective pulse loads duringan active portion of the load switching cycle; and

the respective storage capacitor being configured for supplying thestored energy via the respective to the respective switch power supplyto which the storage capacitor is coupled to each of the pulse loadscoupled to switch power supply during an active portion of the loadswitching cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, an embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 is a schematic representation showing the topology of a prior artpower supply array for feeding a pulse load;

FIG. 2 is a table showing typical operating parameters for the powersupply array illustrated in FIG. 1;

FIG. 3 is a schematic representation showing the topology of a powersupply array for feeding a pulse load according to an embodiment of theinvention;

FIG. 4 is a table showing typical operating parameters for the powersupply array illustrated in FIG. 2;

FIG. 5 is a block diagram showing functionality of a controlled powersupply according to an embodiment of the invention for use in the powersupply array depicted in FIG. 2;

FIG. 6 is a high level circuit diagram showing details of the controlledpower supply depicted functionally in FIG. 5;

FIGS. 7 a to 7 d are graphical representations showing current andvoltage waveforms associated with the controlled power supply shown inFIG. 5 all drawn to a common time scale;

FIG. 8 is a timing diagram of the voltage waveform at the input of theDC-DC converters connected to antenna elements shown in FIG. 7 a;

FIG. 9 is a timing diagram of the current waveform fed to the pulsedload shown in FIG. 7 c; and

FIG. 10 is a timing diagram of the input current waveform to theregulator shown in FIG. 7 d.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description of an embodiment of the invention,components that are common to the power supply array 10 described abovewith reference to FIG. 1 or serve a common function thereto will beidentified by identical reference numerals.

FIG. 3 shows the topology of a power supply array 20 according to theinvention for feeding DC power to antenna elements 11 (constitutingpulse loads) of a phase array antenna. Thus, here also, four antennaarrays are provided each on a respective wall 12, there being one wall12 for each surface of the aircraft as explained above. Each wall 12comprises an array of low voltage current sources 18 that are energizedby high voltage power supplies at a voltage of 270V and each of whichserves as a constant DC current source for feeding constant current at anominal voltage of 70V to a respective storage capacitor 19 each coupledto a plurality of switch power supplies 14. Each of the storagecapacitors 19 serves as a voltage reservoir for storing energy during aninactive portion of a load switching cycle of the switch power supplies14 to which it is coupled when the antenna elements 11 are inactive andfor supplying stored energy to the antenna elements 11 during an activeportion of the load switching cycle. Each of the switch power supplies14 has a respective output capacitor 17 that feeds voltage to therespective antenna element 11 that serves as a pulse load. The currentsources 18 and the switch power supplies 14 cooperate as a controlledpower supply for supplying bursts of substantially constant voltage ofmagnitude 8.7V to each antenna element 11 (constituting a switched load)via the storage capacitor 19 (constituting a voltage reservoir) asdescribed in above-mentioned IL 181843 and as repeated in detail belowwith reference to FIGS. 5 to 10 of the drawings.

FIG. 4 is a table showing a breakdown of the operating parameters of thepower supply array 20 shown in FIG. 3. Thus, starting from the bottom ofthe table each wall 12 accommodates a single phase array antenna, thusresulting in a total of four phase array antennas. Each of the fourwalls 12 houses six low voltage current sources 18, thus resulting in atotal of 24 low voltage power supplies 18. Each of the 24 low voltagepower supplies 18 is coupled to 432 switch power supplies 14, thusresulting in a total of 10368 switch power supplies 14. Each of theswitch power supplies 14 supplies a single antenna element 11, thusresulting in a total of 10368 antenna elements 11, i.e. the same numberas in FIG. 1 thus providing a fair comparison between the arrangementshown in FIG. 3 with that of FIG. 1. It is thus to be noted at theoutset that each switch power supply 14 operates a single antennaelement 11 unlike the arrangement shown in FIG. 1 where each switchpower supply 14 operates 16 antenna elements 11. Consequently, in thearrangement shown in FIG. 2, a failure in a switch power supply 14 willresult in only a single antenna element 11 becoming inoperative. Insaying this, it is to be noted that while this clearly represents asignificant advantage over the topology shown in FIG. 1, the inventionalso contemplates that multiple antenna elements 11 may be shared by asingle switch power supply 14. It will emerge from the followingdiscussion that unlike the conventional arrangement shown in FIG. 1, theinvention renders practical the possibility of powering each singleantenna element 11 by a single switch power supply 14. However, it is ofcourse feasible to share two mutually opposing antenna elements 11between a single switch power supply 14 so that in the event of afailure in the switch power supply 14, only a single antenna element inthe active phase array will be adversely affected. Likewise, a singleswitch power supply 14 may be used to supply power to more than twoantenna elements 11 that are in different phase arrays and/or areotherwise so distributed so that the overall deterioration to each phasearray consequent to a faulty switch power supply 14 will be minimal.

FIG. 4 is configured in an identical manner to FIG. 2 and will thereforenot be described in detail other than to remark that the first line ofthe table (TR) shows the operating parameters of each antenna element 11(constituting a pulse load) assuming an input voltage (Vin) of 8.7V andan input current (Iinp) of 9 A. Once the operating parameters of eachantenna element 11 within each switch power supply 14 are determined, wecan now work our way down the table and compute the operating parametersof the switch power supplies 14, then of each low voltage current source18, then of each wall 12 and finally of the complete power supply array20. Since the results are tabulated in FIG. 4 and a detailed explanationof their derivation has already been presented with reference to FIG. 2,no further description will be given.

If the tables shown in FIGS. 2 and 4 are compared, it emerges thatalthough the same number (10368) of antenna elements 11 are powered inthe arrangements of FIGS. 1 and 3, respectively, in the power supplyarray 20 shown in FIG. 3, the input power (Pin_p) delivered by eachcurrent source (LVPS-CS) to 27 low voltage SPS's 14 is 5,618W and issubstantially constant with time as compared with the much higher46,817W required by the high voltage power supplies 13 of FIG. 1. Thus,assuming that the storage capacitor has an initial voltage of 70V, apermitted voltage drop of 50V and a 100 μs pulse width and assumingSPS's efficiency η of 85%, then using equation (5), it can be shown thatthe value of the required storage capacitor for each array of 27 SPS'sis given by:

$\begin{matrix}{C = {{\frac{5,618*100*0.85}{0.5*\left( {70^{2} - 20^{2}} \right)}\mu\; F} = {212.5\mspace{14mu}\mu\; F}}} & (9)\end{matrix}$

Likewise, assuming that the output capacitor 17 for each switch powersupply 14 having an output voltage of 8.7V may be subjected to a voltagedrop of 0.5V and a 15 μs recovery time the value of the output capacitor17 is given by:

$\begin{matrix}{C = {{\frac{78*15}{0.5*\left( {8.7^{2} - 8.2^{2}} \right)}\mu\; F} = {278\mspace{14mu}\mu\; F}}} & (10)\end{matrix}$

It thus emerges from FIGS. 3 and 4 that by feeding constant current atlow voltage to a storage capacitor during the inactive part of the loadswitching cycle, sufficient voltage can be stored to completely supplypower to the antenna elements. Moreover, the equivalent input capacitorto the switch power supplies for a pulse power level of 46,817 watts isnow C=278*6=1,668 μF (at a voltage level of 70V) instead capacitor valueof 10,238 μF (at a voltage level of 270V) required by the conventionalsolution, the stored energy thus being reduced by a factor of about 600.

This having been explained, we will now describe with reference to FIGS.5 to 11 a circuit for realizing the switch power supply 14 in FIG. 3.

FIG. 5 illustrates a controlled power supply arrangement 14 forsupplying bursts of substantially constant voltage from a voltage source21 to a switched load 22 via a controlled load switch 23, in accordancewith an embodiment of the present invention. In the case where the pulseloads are antenna elements of a radar phase array, the voltage source 21may, for example, be a system supply bus having a rectified linevoltage. It could equally well be a bank of batteries configured toprovide a required line voltage. An input of a switching converter 24(constituting a DC current source) is connected to the voltage source 21via an optional input filter 25. An output of the switching converter 24is connected to a voltage regulator 26 whose output is connected to anoutput capacitor 27 connected across the switched load 22. The switchingconverter 24 includes as part of its output a voltage reservoir forstoring voltage, which for the sake of explanation is shown as a storagecapacitor 28 that is external to the switching converter 24. Theswitching converter 24 may be a Buck or Boost Converter as explainedabove and includes a switching element constituted by a PWM switch 29that is controlled by a PWM controller 30. The PWM controller 30 isresponsive to a first voltage reference V_(REF1) for varying the averageoutput voltage fed to the storage capacitor 28, which stores energyduring that portion of the duty cycle when the PWM switch is ON. Thestorage capacitor 28 feeds voltage to the voltage regulator 26, whichensures that the voltage across the output capacitor 27 remainssubstantially constant and thus able to provide voltage to the load 22whenever the load switch 23 is closed.

The voltage regulator 26 is a DC/DC variable input constant output(VICO) device and ensures that the voltage across the output capacitor27 remains substantially constant. Under such circumstances, the energythat is fed to the load 22 when the load switch 23 is closed iseffectively supplied by the storage capacitor 28, since, even when theload switch 23 is closed, the voltage across the output capacitor 27remains almost constant. Thus most of the energy supplied to the load 22emanates from the voltage stored in the storage capacitor 28 during thatportion of the duty cycle when the PWM switch 29 is ON. The storagecapacitor 28 thus constitutes a voltage reservoir for feedingsubstantially constant voltage to the load 22.

The power supply 14 operates to charge the storage capacitor 28continuously during an inactive portion of the switching cycle of theload switch 23 when the load switch 23 is open, so that sufficientvoltage is stored in the storage capacitor 28 to supply the load 22during an active portion of the switching cycle when the load switch 23is closed. Since the power supply arrangement 14 is intended forsupplying short, intermittent voltage bursts to the load 22, theinactive portion of the switching cycle is much longer than the activeportion. In other words, the load switch 23 has a low duty cycle. Thisallows energy to be stored continuously and gradually during theinactive portion of the switching cycle at a rate that ensures thatsufficient voltage is stored in the storage capacitor 28 to supply theload 22 while avoiding sudden voltage surges that would give rise tocorresponding drop in the line voltage. This requirement is net by anaverage current processing unit 33 that does two things. First, based ona predetermined current that is to be sourced by the load 22 during theactive portion of the switching cycle of the load switch 23, it computesan average current that should be fed to the storage capacitor 28 duringthe much longer inactive portion of the switching cycle to ensure thatsufficient energy will be stored in the storage capacitor 28 to supplythe load without completely draining the storage capacitor 28. Thepredetermined current may be computed or estimated based, for example,on previous load characteristics. Secondly, the average currentprocessing unit 33 controls the duty cycle of the PWM switch 29 in theswitching converter 24 so as to feed the computed current to the storagecapacitor 28. In a practical implementation of the invention, theaverage current processing unit 33 may be a computer that controls theload switch 23, as well as the PWM switch 29, and which also determinesthe voltage to be fed to the load 22 as well as the duty cycle of theload switch 23 needed to achieve this voltage.

The manner in which the required control of the switching converter 24is performed is as follows. A current sensor 34 senses the DC current atthe output of the switching converter 24 and a current-to-voltageconverter 35 coupled to the current sensor 34 produces a correspondingvoltage that is proportional to the measured current. The averagecurrent processing unit 33 operates to feed the resulting voltage to thenegative input an error comparator 36, whose positive input is connectedto a second voltage reference, V_(REF2). The error comparator 36 thusproduces at its output a signal that is a function of the differencebetween the current produced by the switching converter 24 and a desiredreference current and serves as a feedback signal for ensuring that theswitching converter 24 operates at a desired constant current.

The output of the error comparator 36 is fed to a first input of aweighting unit 37 constituted by an adder whose second input isconnected to the output of a feedback circuit 38 whose input isconnected to the storage capacitor 19. The weighting unit 37 thusreceives two voltage signals, one of which is a function of the voltageacross the output capacitor 17 and the other of which is a summingfunction of the reference V_(REF1) and the current produced by theswitching converter 24 measured by current transformer 34. The referenceV_(REF1) is generated by calculating the difference between the averagecurrent measured by current transformer 34 and the output of theweighting circuit 37, that is equal to the PWM voltage referenceV_(REF1) (corresponding to pin 2 of the PWM controller 30 in FIG. 6).The weighting unit 37 sums these two voltage signals and feeds theresulting weighted voltage signal to the negative input of a PWM errorcomparator 39 (corresponding to pin 1 in the PWM controller 30), towhose positive input is connected the first voltage reference V_(REF1).The output of the PWM error comparator 39 is thus a function of thedifference between the first voltage reference V_(REF1) and the weightederror signal derived by the weighting unit 37. The PWM controller 30 isresponsive to the output of the PWM error comparator 39 for adjustingthe duty cycle of the PWM switch 29. The duty cycle of the PWM switch 29determines the extent to which the storage capacitor 19 is charged. Asnoted above, the storage capacitor 19 should be sufficiently chargedthat it maintains some residual voltage during the active portion of thecycle when the load switch 23 is closed. To achieve this requirement,the weighted error signal balances the feedback signal indicative of thevoltage across the storage capacitor 19, whereby the duty cycle of thePWM switch 29 is adjusted to ensure that the output of the switchingconverter 24 will adequately charge the storage capacitor 19, duringboth the active and inactive portions of the cycle. This ensures thateven during the active portion of the cycle when the load switch 23 isclosed, the load 22 does not use all the energy stored in the storagecapacitor 19 so that some residual voltage is always left in the storagecapacitor 19. Were this not done, any slight voltage shortfalls wouldaccumulate over time thus leading to the eventual failure of the storagecapacitor 19 to provide sufficient voltage to the load 22 during theactive portion of the cycle. Moreover, owing to the described operationof the weighting unit 37, the voltage fed to the load 22 is essentiallysupplied completely by the storage capacitor 19 and the voltage acrossthe output capacitor 17 is substantially constant throughout the wholeswitching cycle.

The controlled switch power supply 14 (FIG. 3) thus operates to ensurethat the energy supplied to the load 22 during the active portion of theswitching cycle is stored by charging the storage capacitor 19 graduallyat a constant current whose magnitude is adjusted by the average currentprocessing unit 33 (FIG. 5) based on the power to be fed to the load 22during a subsequent active portion of the switching cycle. This avoidssudden current surges on the input voltage source and avoids the needfor a bulky RFI filter at the input of the power supply.

Having described the principle of operation, there will now be describedwith reference to FIG. 6 a high level circuit diagram showing details ofthe controlled power supply 14 described functionally with reference toFIG. 5. The intention of FIG. 6 is to present how the components shownfunctionally in FIG. 5 can be implemented in practice. Therefore, onlythe most salient features will be described since the circuit diagramprovides a fully enabling disclosure sufficient for one skilled in theart to carry out the invention.

Thus, the heart of the controlled power supply 14 is an SG1825controller 30 which controls the switching converter 24 and constitutesthe PWM controller 30. The first voltage reference V_(REF1) is fed to avoltage reference terminal (pin 16) thereof and positive and negative DCpower supply rails are connected respectively to the Vcc and GNDterminals (pins 13 and 12, respectively). The load current is sensed viathe current transformer 34 across which are connected respective sourceterminals of a pair of MOSFET switches 41 a and 41 b whose drainterminals are commonly connected to a coil 32 that is part of theswitching converter 24 and is connected to GND via the storage capacitor19. The respective gate terminals of the MOSFET switches 31 a and 31 bare controlled by respective drivers 35 a and 35 b, that receive drivesignals via the PWM output pins (11) and (14) of the SG1825 controller30. The MOSFET switches 31 a and 31 b thus operate as the PWM switch 29shown in FIG. 5.

For the sake of clarity the current transformer 34 is shown twice in thefigure, i.e. in addition with regard to its connection to the SG1825controller 30, it is also shown with regard to its signaling. Thus, itsoutput representative of the current sensed by current transformer 34 iscoupled via a pair of rectifier diodes D1 and D2, whose respectivecathodes are commonly connected to a resistor R6, across which there isthus produced a voltage that is proportional to the current sensed bycurrent transformer 34. The resistor R6 thus functions as thecurrent-to-voltage converter 35 shown in FIG. 5. The positive terminalof the resistor R6 is connected to the positive input of an OP AMP 46 towhose negative input is fed the reference voltage V_(REF2) via aresistor R10. The reference voltage V_(REF2) is derived at the output ofan OP AMP 36 that is connected as an inverting amplifier whose input isfed to a variable DC source. A capacitor C12 and a resistor R3 areconnected between the negative input and the output of the OP AMP 46.The OP AMP 46 thus operates as an integrator and functions as theaverage current processing unit 33 shown in FIG. 5. In accordance withone embodiment, the values of the capacitor C12 and the resistor R10 areselected to set the integration averaging interval to be one order ofmagnitude larger than the largest expected pulse load interval.

The output of the OP AMP 46 is fed to a variable resistor VR1 connectedto the anode of a rectifier diode D5, whose cathode is coupled to theinverting input (pin 1) of the SG1825 controller 30. The feedbackvoltage at the input of the voltage regulator 26, is coupled to thepositive input of an OP AMP 38 that is configured as a feedbackamplifier and is functionally equivalent to the feedback loop 38 shownin FIG. 5 through a level adaptor 47 connected as a voltage buffer whoseoutput is coupled via a resistor R1 to the cathode of the rectifierdiode D5 and thence to the inverting input of the SG1825 controller 30.The combination of the resistors R1 and VR1 together with the rectifierdiode D5 thus functions as the weighting unit 37 shown in FIG. 5, whoseoutput is the sum of the feedback voltage 38 and the output of the OPAMP 46, corresponding to the average current processing unit 33 shown inFIG. 5.

Pins 5 and 6 of the controller 40 allow for connection of externaltiming components R_(T) and C_(T) constituted by a resistor R20 and acapacitor C11 for adjusting the frequency of an internal oscillator. Pin8 of the SG1825 controller 40 is a soft-start input that is held lowwhen either the controller is in the micro-power mode, or when a voltagegreater than +1.4 volts is present on pin 9. Thus, by applying a voltagesignal of sufficient amplitude across the diode D4, the optocoupler U3feeds a shut down signal via diode D3 to pin 9 of the controller.

FIGS. 7 a to 7 d are graphical representations showing current andvoltage waveforms associated with the controlled power supply shown inFIG. 5 all drawn to a common time scale.

FIG. 8 is a timing diagram of the voltage waveform at the output of theswitching converter. This corresponds to the waveform across the storagecapacitor 19 as shown qualitatively in FIG. 7 a. However, the time basein FIG. 7 a is much more spread out in that the time for the voltage tofall from 101V to 82V is seen in FIG. 8 to be approximately 0.1 ms,which indicates that FIG. 7 a shows the voltage only over a period ofapproximately 0.25 ms of which approximately 0.12 ms relates to thesubsequent voltage increase, shown only partially in FIG. 7 a. The timefor the storage capacitor 28 to fully charge to its full voltage of 101Vis seen in FIG. 8 to be just under 1 ms. This implies that onlyapproximately 1-tenth the charging cycle is shown in FIG. 7 a.

FIG. 9 is a timing diagram of the current waveform fed to the pulsedload 22 as shown qualitatively in FIG. 7 c; and FIG. 10 is a timingdiagram of the input current waveform to the regulator 26 as shownqualitatively in FIG. 7 d. It emerges from a comparison of the timebases of FIGS. 9 and 10 with that of FIG. 7 a that the pulse widths havean approximate duration of 0.1 ms (i.e. the time for the voltage acrossthe storage capacitor 19 to fall from 101V to 82V), which isapproximately 1-tenth of the duty cycle.

It thus emerges from the above discussion that the storage capacitor 19is charged gradually over nine-tenths of its duty cycle and dischargedabruptly across the load 22 for only one-tenth of the duty cycle, sothat it stored voltage falls only from approximately 101V to 82V, thusmaintaining most of its charge. By such means the load on the inputremains substantially constant.

Although the invention has been described with particular regard to useof a DC power supply for supplying power to the load, it will beunderstood that a rectified AC power supply may also be used.

It will be understood that while the specific phased array antennadescribed above has four walls, in practice a different number of wallsmay be used so long as a required field of view can be achieved usingall the walls.

Likewise, while the invention has been described with particular regardto supplying power to antenna elements of a phased array antenna, itwill be appreciated that the principles of the invention may findapplication also with regard to other types of pulse load, particularwhere a plurality of pulse loads must be sequentially energized atdifferent points of a supply cycle.

1. A method of supplying bursts of substantially constant voltage to aplurality of pulse loads, the method comprising: providing an array oflow voltage current sources, each for feeding constant DC (DirectCurrent) current at a nominal voltage to a respective storage capacitor,each of which is coupled to a plurality of switch power supplies;coupling each of the switch power supplies to a respective outputstorage capacitor for feeding voltage to the pulse load; storing energyin each of the storage capacitors during both active and inactiveportions of a load switching cycle of the respective switch powersupply, to which the corresponding storage capacitor is coupled, forfeeding voltage to the respective pulse loads during an active portionof the load switching cycle; and supplying the energy, stored in therespective storage capacitor to the respective switch power supply, towhich the storage capacitor is coupled, and then to each of the pulseloads during the active portion of the load switching cycle, wherein thesupplying of said energy comprises computing an average current thatshould be fed to the respective storage capacitor in order to ensurethat sufficient energy will be stored in said respective storagecapacitor to feed the pulse load without substantially completelydraining said respective storage capacitor.
 2. The method according toclaim 1, wherein supplying the energy stored in the respective storagecapacitor to the respective switch power supply comprises: supplyingcontinuous energy to the respective storage capacitor at a substantiallyconstant current equal in magnitude to the average current.
 3. Themethod according to claim 1, further comprising: feeding energy to therespective storage capacitor via a switching converter; and varying aduty cycle of the switching converter to produce a desired averagecurrent.
 4. The method according to claim 3, further comprising: varyingthe duty cycle of the switching converter so as to maintain the currentsupplied by the switching converter at a level slightly above an averagecurrent required by the pulse load.
 5. The method according to claim 3,further comprising: setting an integration averaging interval of theswitching converter to be an order of magnitude larger than a largestexpected pulse load interval.
 6. The method according to claim 1,wherein a single pulse load is coupled to each of the switch powersupplies.
 7. The method according to claim 1, wherein at least two ofthe pulse loads are coupled to each of the switch power supplies.
 8. Themethod according to claim 1, wherein the pulse loads are antennaelements of a phased array antenna.
 9. A controlled power supplyconfigured to supply bursts of substantially constant voltage from arespective storage capacitor to a plurality of pulse loads via a loadswitch, said power supply comprising: an array of low voltage currentsources, each for feeding constant DC (Direct Current) current at anominal voltage to a respective storage capacitor; a plurality of switchpower supplies coupled to each of the storage capacitors and torespective pulse loads; each of the storage capacitors being configuredfor storing energy during both active and inactive portions of a loadswitching cycle of the respective switch power supply, to which thecorresponding storage capacitor is coupled, when the pulse loads areinactive; a respective output storage capacitor in association with eachof the switch power supplies for feeding voltage to the respective pulseloads during an active portion of the load switching cycle; therespective storage capacitor being configured for supplying the storedenergy to the respective switch power supply, to which the storagecapacitor is coupled, and then to each of the pulse loads, during theactive portion of the load switching cycle; and an average currentprocessing unit responsive to a predetermined current that is to besourced by the pulse load during the active portion of the loadswitching cycle for computing an average current that should be fed tothe respective storage capacitor to ensure that sufficient energy willbe stored in said respective storage capacitor to feed the pulse loadwithout substantially completely draining said respective storagecapacitor.
 10. The controlled power supply according to claim 9, whereinfor each of the switch power supplies there is comprised: a controlleroperatively coupled to the average current processing unit configured tosupply continuous energy to the respective storage capacitor at asubstantially constant current equal in magnitude to said averagecurrent and configured to generate switching signals for closing andopening said load switch at a rate and duty cycle that is commensuratewith respective durations of the active portion and the inactive portionof the switching cycle.
 11. The controlled power supply according toclaim 10, further comprising in respect of each controller: a switchingconverter controlled by a PWM switch for coupling to a voltage sourceand producing an output voltage; and a storage capacitor for storingenergy and for supplying the stored energy to the load during the activeportion of the load switching cycle; said controller being coupled tothe switching converter for pulse width modulating the PWM switch. 12.The controlled power supply according to claim 9, wherein: the averagecurrent processing unit comprises an integrator having a capacitor and aresistor selected so as to set an integration averaging interval of theintegrator to be an order of magnitude larger than the largest expectedpulse load interval of the switching converter.
 13. The controlled powersupply according to claim 9, wherein a single pulse load is coupled toeach of the switch power supplies.
 14. The controlled power supplyaccording to claim 9, wherein at least two of the pulse loads arecoupled to each of the switch power supplies.
 15. The controlled powersupply according to claim 9, wherein the pulse loads are antennaelements of a phased array antenna.
 16. A phased array antenna systemcomprising: a plurality of modules each containing a plurality ofantenna elements adapted to scan over a predetermined field of view; anda respective controlled power supply, according to claim 15, forsupplying power to the antenna elements in each module.